Github user ueshin commented on a diff in the pull request:
https://github.com/apache/spark/pull/21704#discussion_r200125302
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala
---
@@ -2007,7 +2007,14 @@ case class Concat(children: Seq[Expression]) extends
Expression {
}
}
- override def dataType: DataType =
children.map(_.dataType).headOption.getOrElse(StringType)
+ override def dataType: DataType = {
+ val dataTypes = children.map(_.dataType)
+ dataTypes.headOption.map {
+ case ArrayType(et, _) =>
+ ArrayType(et,
dataTypes.exists(_.asInstanceOf[ArrayType].containsNull))
--- End diff --
I guess the inner nullabilities are coerced during type-coercion? If the
inner nullabilities are different, type coercion adds casts and they will
remain.
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